The present invention relates generally to electrical medical leads, and more particularly to stimulation leads of the type which dispense a steroid or other drug adjacent the stimulation site. The invention is particularly useful in the context of a cardiac pacing lead.
Delivery of a drug at the stimulation site of an implantable pacing lead is disclosed in U.S. Pat. No. 4,711,251, for a "Body Implantable Lead", issued to Stokes on Dec. 8, 1987, and incorporated herein by reference in its entirety. A particularly desirable configuration for such a lead is disclosed in U.S. Pat. No. 4,506,680, for a "Drug Dispensing Body Implantable Lead", issued to Stokes on Mar. 25, 1985, also incorporated herein by reference in its entirety. In this configuration, the drug to be dispensed is a steroid compounded with silicone rubber based medical adhesive to form a monolithic controlled release device (MCRD). The MCRD is located in a chamber within the stimulation electrode, and elutes out of the electrode through a porous elution path. The steroid acts as an antiinflammatory agent, reducing the adverse reaction of the tissue to the stimulation electrode.
Alternative embodiments of stimulation electrodes which elute a steroid or other drug are disclosed in U.S. Pat. No. 4,606,118, issued to Cannon et al and in U.S. Pat. No. 4,577,642, issued to Stokes. A myocardial pacing lead adapted to deliver steroid at the stimulation site is disclosed in Statutory Invention Registration No. H356. In this lead, a steroid is delivered through a barbed electrode to a delivery point within the myocardium.
Use of a fixation helix to attach a pacing or other stimulation electrode to tissue to be stimulated is disclosed in U.S. Pat. No. 4,046,151, issued to Rose. In this lead, the fixation helix is fixed with respect to the lead body and acts as the stimulation electrode. The fixation helix is shielded by a collapsible sheath which surrounds the helix until it is screwed into the tissue to be stimulated. An alternative design employing a fixation helix which functions as an electrode is disclosed in U.S. Pat. No. 4,282,885 issued to Bisping. In this lead, a plug or plunger is located within the helix, extending past the sharpened distal end of the helix. After the lead reaches the stimulation site, the plunger may be pulled into the distal end of the lead, allowing the electrode to be screwed into the tissue. The plunger is retracted by means of a stylet or wire which appears to be permanently affixed thereto.
An endocardial pacing lead in which the fixation helix is not used as an electrode is disclosed in U.S. Pat. No. 4,146,036 issued to Dutcher et al. In this lead, a separate electrode is provided at the distal end of the lead body. The fixation helix is shielded during introduction and passage to the stimulation site by means of a plunger slidably located within the helix. The plunger is advanced by means of a removable stylet. The lead is provided with a resilient plastic member which automatically retracts the plunger when the stylet is removed.
Yet another endocardial pacing lead employing a fixation helix is disclosed in German Patent Application No. 330,050 by Botvidsson et al. In this lead, a stylet is used to advance the electrode past the distal end of the helix to prevent damage due to the helix during passage of the lead to the stimulation site. Retraction of the electrode into the distal end of the lead body to expose the helix is accomplished by means of a resilient elastic member, similar to the mechanism for retracting the plunger described in the above-referenced Dutcher et al patent.